﻿<!DOCTYPE html>
<html>
<head>
<metacharset="utf-8" />
<title></title>
<style>
body{margin:0; padding:0;}
#run{width:100px; height:100px; background:#06c; position:absolute; border:1px solid #000; opacity:0.3; filter:alpha(opacity=30);}
</style>
<script>
window.onload = function(){
  var run = document.getElementById("run");
  var btn = document.getElementById("btn");
  var speed = 1;
  var timer = null;
  var alpha=30;
  run.onmouseover = function(){
    startrun(100);
  }
  run.onmouseout = function(){
    startrun(30);
  }
  function startrun(target){
    clearInterval(timer);
    timer = setInterval(function(){
      if(target > alpha){
        speed = 2;
      }else{
        speed = -2;
      }
      
      if(alpha == target){
        clearInterval(timer);
      }
      else{
        alpha = alpha + speed;
        run.style.filter = 'alpha(opacity='+alpha+')';
        run.style.opacity = alpha/100;
        document.title = alpha;
      }
    },30)
  }
}

</script>
</head>

<body>
<div id="run"></div>
</body>
</html>